The present invention provides improvements in changeable signs. One of the inventors of this application, Fred. M. Black, is the inventor of U.S. Pat. No. 4,761,905 entitled "Scanned Electromechanical Display" and U.S. Pat. No. 4,912,442 entitled "Scanned Electromechanical Alphanumeric Display Apparatus". The co-inventors of this application, Fred. M. Black and G. Frank Dye are the co-inventors of U.S. Pat. No. 5,412,891 entitled "Changeable Sign". The disclosures of these three patents are hereby incorporated herein by reference. The '905 and '442 patents provide a description of certain of the prior art in the field of the present invention.
The cited patents disclose sign elements which can display alphanumeric or graphical information, through the selective arrangement of individual pixels. The pixels are rotatably mounted elements having multiple display faces, only one of which is noticeable to an observer at a time. The overall pattern of pixel display faces comprises the alphanumeric or graphical indicia of the sign. These prior patents disclose arrays of such pixels and actuator devices which pass behind the arrays to selectively rotate the pixels, causing a new display face of a rotated pixel to be noticeable and, thus, changing the displayed indicia of the sign. The present invention has these notions in common, but provides improved design features to create a superior product.
More specifically, the '442 patent disclosed a display apparatus having a plurality of rotationally mounted display elements that are arranged into a grid matrix of rows and columns, each display element having first and second display faces perpendicular to each other and joined along respective adjacent edges. Each display element also has first and second ramp surfaces rigidly connected along inside edges of and extending substantially away from a back surface of the first and second faces. The display apparatus also includes a series of solenoids, which strike the ramp surfaces of the display elements, causing the display elements to rotate 90 degrees. The solenoids are mounted on a carriage that moves bidirectionally on a horizontal path behind the display apparatus. The carriage has wheels attached to the top and bottom, which ride along tracks at the top and bottom of the display apparatus.
The grid configuration of the '442 display apparatus is modular only in the horizontal direction and, thus, modules must be built to the full height of the sign. Likewise, the sign uses a single carriage, which is also built to the full height of the sign. Thus, construction of the grid and carriage is difficult, costly, and inflexible. A set of modules only permits constructing signs of a single height.
The single carriage of the '442 display apparatus is driven by a dual cable drive system, having independent drums and cables on the top and bottom. The two sets of drums and cables must be precision machined and matched in order to prevent the carriage from skewing from vertical when traversing behind the pixel elements.
The electronics controlling the solenoids in the '442 apparatus cause the solenoids to fire and release for each pixel. The voltage applied to each solenoid causes peak currents in excess of seventeen amps (at 13.5 V) and average currents of over 10 amps. A commercially useful apparatus requires solenoids with lifetimes in excess of five million cycles, which is considerable, given these circumstances, so that early failure can be a problem.
The shape and mounting of the pixels was a major improvement introduced by the '891 patent. The display faces were designed to be cylindrically concave, with the axis of concavity being parallel to the pixel's axis of rotation. Also, the ramp surfaces were given different configurations. These modifications allowed the pixels to be arranged in closer proximity to one another. The pixels included a hub that was mounted to a wire that served as the axis of rotation and was suspended between two vertical supports. However, the pixel design was still complex and did not assure reliable transitions from one display state to the other.
Thus, there exists a need for a scanned pixel sign that is more versatile, sturdier, less costly, and has a reliably longer commercial lifetime.